Why the best part of your brain is hiding under the stairs

Harry Potter wasn’t the only amazing thing to come out of the cupboard under the stairs. It’s said that art mimics nature, and in this case, the result is absolutely fascinating (to me).

How quickly can you get up to speed?

Let’s quickly recap evolutionary theory. For those of you who struggle with evolution due to your personal or spiritual beliefs (and this article may be harder to assimilate than others), perhaps you might be interested in skipping over the following and instead checking out the science behind speaking in tongues. Evolutionary theory holds that over time certain physical and psychological traits perform better in the environment than others. So as an extraordinarily hyperbolic example, consider an animal that ranges in colour from green to yellow. It lives in a green bush, so being more green means you’re less likely to be seen and eaten by predators. As a result, over a period of time, fewer yellow versions of the animals are around to mate with other yellow versions and as a result, one day only the green variants remain. With me so far? This process is commonly known as adaptive selection. The trait that is more adaptive is selected for over that which is less adaptive.

Don’t get too excited. The process often takes many thousands of years. So it’ll be a little while before BMW drivers get wiped out in favour of people who are actually good at driving.

Adaptive selection is problematic

One of the problems with adaptive selection is that it’s hard to explain everything in terms of some adaptive benefit. It’s easy to say that having thumbs is way better than having an extra finger instead. Other things are harder to explain, like belly buttons, or pubic hair. These things are often thought of as by-products of adaptations. For example, belly buttons are the by-product of the adaptive umbilical cord. Pubic hair is a remnant of our hairy past. These no longer serve an adaptive function (that we know about).
So why are they still here? That’s the rub. One logical answer is that while they serve no adaptive function, they also serve no maladaptive function. Consider our hypothetical animal. Being yellow was maladaptive – you get eaten. But let’s say our animals also have black spots. Not super helpful in a green bush, but not really unhelpful either. It doesn’t help them blend in, but doesn’t make them stand out. So the black spots will get passed down the line. Neither selected for or against.

By-products can be adaptive

This is the fun part. First, a lesson in architecture. Do you know what a spandrel is? Most people probably wouldn’t. If you decide to build an archway in your doorframe, you’re left with empty space where the corner usually is. That’s a spandrel. Now, artists are quite averse to empty spaces, so back when arches were a big architectural deal, people started filling those spandrels with artwork. All of a sudden, useless empty space because something beautiful and useful.

Now that’s a damn spandrel and a half. See the triangular shapes in the top right and top left corners? Those are spandrels. I’m not enough into architecture to know whether the rest of the decoration would be called that. Nor to know where this is. Looks Moorish. Do a search and get back to me.

Let’s try a more modern example. When humans started building stairs, we simultaneously became annoyed by the empty space that was used up because of the staircase. Thus the birth of the cupboard under the stairs. All of a sudden, useless space becomes useful (especially once you put Mr Potter in there).

Brains have heaps of useless space

Human brains are enormous and we don’t really understand why. We can explain some of this in terms of processing power. Just like a computer, the bigger the size, the better the processing power. We can kind of measure this with the ‘encephalisation quotient’ (EQ). That is essentially how big your brain is vs how much body mass you have. The bigger the brain in relation to your mass, the smarter you probably are in comparison to other animals around that size. If you graph it, you can see that the more successful animals tend to have a higher EQ. But this only goes so far. Eventually, the EQ stops having any explanatory power. Especially when you look at humans. Look at the below (sorry for the ugly science graphs, both from this paper by Roth and Dicke – it’s just that they’re nice and clear). In the first we can see that the classically ‘smarter’ animals are way above the line – what we might expect as the average brain to body size. But it’s well known that as we move toward the larger end of the scale, it starts to be a less useful measure. In the second graph, look at the brain volume measured against the body weight for some typical primates. Look how damn enormous our brain is in comparison to our smartest brethren (loosely speaking), the chimpanzees. And look how quickly the size ratcheted up. We’re not entirely sure which of the green line we might have descended from, but our brains sure grew fast from one iteration of humanoid to another. Surely processing power couldn’t explain this benefit entirely, or why wouldn’t all apes have EQ’s as big as us?

Well, it might very well be that the human brain is full of spandrels. Think about the computer. It was developed for some very specific purposes. Computing big numbers, storing data and so on. In fact, we buy a computer for very specific functions. I mostly use mine for word processing. But the power of the computer lends itself to far more uses than it’s original design, and so we used that power to create computer games and all sorts of other things that never crossed the minds of the original inventors. If our brain is full of by-products that by happy accident we managed to make useful, then it would certainly explain why our brains got so big, so quickly.
Language is one of the most commonly cited examples of a possible brain spandrel. Almost all animals communicate to some degree. Communication is fantastically useful. But to knowledge, no animal really communicates like humans do. So much of what we talk about is adaptively useless. It might very well be that the size of our brain allowed language to blossom from the communication of ordinary and important information into something far greater. Eventually, language in this new, expanded form became useful in and of itself. And so, our brains continued to grow to accommodate the useful properties of this thing that was originally a useless byproduct. That might have led to writing. Again, plenty of animals leave communication marking on things (think of the dog marking it’s territory). But nothing else writes down stories and memories. Think how useful these by-products have been (if they are indeed by-products). No wonder our brains grew so fast.Evolution does weird things to our bodies. For instance, did you know that our bodies treat rejection the same as physical pain? It’s the same reason that you would probably jump off a bridge if everyone else was doing it (contrary to your mama’s advice). Turning scholarship into wisdom without the usual noise and clutter, we dig up the dirt on psychological theories you can use. Become an armchair psychologist at The Dirt Psychology.

About Dorian Minors

I read and write about cognitive science. Sometimes I train honeybees. I promise they're related. I made this site so that you wouldn't have to figure out whether you should care about the difference between non-conscious and a-conscious, or what 'multiplexing' is. My special interests are interpersonal relationships, the science of community, spirituality and the brain, and the neural basis of complex behaviour. I hope this stuff is as interesting to you as it is to me.